What sum of two numbers is 8 and their difference is 12 Find the numbers?

Let X be one number and Y the other. So, X + Y = 8 and X - Y = 12 Solve the set of equations simultaneously or use substitution method. X + Y = 8 X - Y = 12 (ADD THIS EQUATION TO FIRST ONE) _______________ 2X = 20, So X =10 and solving for Y using either equation, Y = -2